Allow MediaProvider to traverse /mnt/media_rw.
As an optimization, platform components like MediaProvider may choose
to shortcut past the FUSE daemon and return open file descriptors
directly pointing at the underlying storage device.
Now that we have a specific label for /mnt/media_rw, we need to grant
search access to untrusted apps like MediaProvider. The actual
access control is still managed by POSIX permissions on that
directory.
avc: denied { search } for name="media_rw" dev="tmpfs" ino=4150 scontext=u:r:untrusted_app:s0:c512,c768 tcontext=u:object_r:mnt_media_rw_file:s0 tclass=dir permissive=0
Bug: 21017105
Change-Id: I6d51939668b39b43b91b1f0c24c98bc2205bf511